This invention relates to wire coiling apparatus for high speed coiling of wire at uniform coiling pressures.
The formation of wire coils on a spinning mandrel (which those in the trade sometimes call an arbor) has been practiced for many years. A few decades ago, this was largely accomplished by the use of a pair of rubber coiling rolls astraddle the mandrel, as set forth for example in my U.S. Pat. No. 2,227,602 (1941). The rubber rolls were driven directly by the mandrel spindle, thereby being in synchronization with the mandrel. Subsequent demands for greatly increased production output from the coiling machines necessitated application of a liquid cooling medium or solution in the zone of the forming coil to dissipate the heat generated. But, such liquid solutions seriously disrupted the frictional grip of the rubber forming rolls on the spindle. Thus, rubber rolls could not be effectively used for many coiling operations. The heat generated as the metal was worked limited the production speed so that the first few turns being formed on the mandrel did not melt the rubber forming surfaces. Rolls of rubber or other resilient compositions also exhibited another fault in that the carefully balanced coiling forces became upset by problems in the infeeding wire, e.g. bends, snarls, and kinks. The wire would wind back on the resilient backup shoulder, causing the wire to "ball up", so to speak, on the mandrel and "chew up" the carefully and accurately ground surfaces of the coiling rolls before the operator could shut the machine off. Unwatched ends of the wire from the pay off spool could produce similar results. In each case, the rolls had to be removed and reground before coiling could resume, thereby causing undesirable down time.
Thereafter, steel coiling rolls driven by flexible drive shafts such as taught in my subsequent U.S. Pat. Nos. 2,868,267, 3,082,810, and 3,401,557, assumed an important position. Cooling solutions could be applied to the coil forming zone without affecting the drive relationship of the coiling rolls. Steel forming surfaces moreover are not readily damaged. Production speeds could therefore be increased. These were used for medium and heavy wire since considerable power could be picked up at the rear of the machine and fed forward via flexible cables and speed reducers to the coiling rolls. But because these rolls of necessity are mounted in hangers, the drive force to one roll, usually the one slightly to the rear, had its drive torque added to the pressure of that roll on the coil being formed, while the drive force to the other roll had its drive torque subtracted from the pressure of this other roll. The resulting unequal pressures can be tolerated while coiling medium to heavy wire, but not on fine wire.
Another approach which was tried is set forth in U.S. Pat. No. 2,909,209 in which a front roll of elastic material was applied to my flexible cable driven machine in a version called a one-sided coiler. Using a one-sided coiler, the wire, typically medium gage (by today's standards) will expand instantly from its grip on the mandrel. Here also, cooling solution was used. However, the unit was a failure unless the coil was stiff enough to retain its true helix with one opposite shoulder backup. It lacked a positive solid shoulder for the first turn of wire on the resilient roll side to prevent wind back. The machine therefore was discontinued.
But, as technological developments have continued in the products for which the wire coils are formed, not only are higher production rates demanded, but also the wire sizes to be coiled covered a broad range from extremely fine diameters, e.g. about the size of human hair to considerably larger diameters. Yet the coils formed have to be uniform in characteristics such as electrical resistivity, pitch, strength and the like. Steel coiling rolls have difficulty coiling fine wire in a manner to meet these high demands. Complete synchronism of the drive shaft-driven steel rolls with the arbor is extremely difficult to achieve, and almost impossible to maintain. The steel rolls moreover do not apply uniform forming pressure required to obtain a uniform coil of fine wire as noted above. The rolls are not sufficiently sensitive to the wire characteristics. I have determined that fine wires, of themselves, cannot form a uniform helix on a mandrel without the first turn of wire having positive unyielding, i.e. inelastic, shoulder support for the front and rear portions of this turn, i.e. from both forming rolls. And the pressure must be uniform. Moreover, the work rolls must be fully synchronized with the mandrel and each other. And they must be sensitive to the wire characteristics. Therefore, there has been a definite need for a wire coiling apparatus not heretofore available.